Impact and mechanisms of film thickness on sensitivity and magnetoresistance of CrO <i>x</i> N <i>y</i> thin-film cryogenic temperature sensor

Abstract

Cryogenic temperature sensing technology under extreme conditions has gathered attention due to its potential applications in various fields such as space exploration and superconductivity research. Under strong magnetic fields, an important extreme condition, CrOxNy stands out as an ideal thin-film material for cryogenic temperature measurement due to its chemical stability and low magnetoresistance. The film thickness, as a parameter, can affect the temperature coefficient of resistance (TCR) and anti-magnetic field ability for CrOxNy thin-film sensors. However, this topic has not been sufficiently explored. In this work, CrOxNy films with different thicknesses (20–151 nm) were fabricated by modulating the duration of DC magnetron reactive sputtering. The results show that thicker films tend to have larger crystal grains and better CrN phase formation. Thinner films exhibit higher sensitivity, higher magnetoresistance, and more temperature measurement error. The sensor with 20 nm-thick films exhibited the highest TCR of 0.36 472 K−1 under 4 K, while a 151 nm-thick sensor showed the lowest temperature measurement shift which under 6 K is down to 8.03 502 mK even under the 9 T magnetic field. Further theoretical analysis reveals that multiple conduction mechanisms exist in fabricated sensors, leading to different electrical and magnetic properties.